Your MacBook already includes everything it needs to protect itself from viruses and malware. It's part of the cost of a Mac. There is no need to purchase anything else.
Most commercial OS X anti-virus utilities are 100% junk and will just separate you from your money.
Your Mac is designed to be used, not pampered. Use it. Keep your system up to date and be vigilant about phishing scams. That is all you need to do to keep your Mac safe.